The explosive growth of telecommunications services and products is fostered by improving features and accessibility. Data connections, such as DSL, have become increasingly popular. On the other hand, plain old telephone service (POTS) has become less relevant to many users.
In order to convey telecommunication signals over a traditional telephone line, telephone companies typically supply tip and ring voltage and loop current to support a number of functions including carrying analog voice signals and performing various signaling functions on the telephone line. To be recognized by various switch equipment, telephone devices connected to POTS telephone lines typically generate tones referred to as DTMF (dual-tone multi-frequency) signals. DTMF signals comprise first and second sine wave signals that are added together to encode the number to be dialed. However, DSL technologies provide significantly greater bandwidth as compared to analog telephone equipment.
There are a number of DSL specifications, including ADSL (Asymmetric Digital Subscriber Line), ADSL-Lite, R-ADSL (Rate Adaptive Digital Subscriber Line), HDSL (High Speed Digital Subscriber Line), SDSL (Symmetrical Digital Subscriber Line), and VDSL (Very High Speed Digital Subscriber Line), which are referred to collectively as DSL technologies. In one of the more popular versions of DSL, ADSL, a twisted pair carries two types of duplexed signals over different frequency bands. The first signal is the voice signal, generally at 4 KHz and below. The second signal is the data signal, generally modulated at above 4 KHz. With the advent of DSL, the traditional tip and ring voltage and loop current functions are increasingly being replaced with high speed digital signals capable of carrying voice, data and video information to and from a subscriber in a digital fashion.
Communications field service technicians maintaining POTS lines traditionally used a test instrument called a phone test set or lineman's handset. The test set is used by the technician in the installation and troubleshooting of analog phone systems. One of the functions performed by field service technicians is to verify that the real physical circuit being tested is actually the circuit with the reported problem before the technician begins to troubleshoot the issue. The conventional phone test set can be used for line identification purposes by attaching to a circuit and dialing a specific phone number that generates an automated response indicating “the number you are dialing from is xxx-xxx-xxxx.” Thus, the telephone number being a unique identifier for the subscriber can help field service technicians to confirm that they identified the correct wire pair from potentially hundreds or thousands of circuits typically present in a junction box. However, with the removal of loop current and ring voltages from existing telephone lines traditional phone test instruments can no longer be used for line identification purposes.
Accordingly, it may be desirable to determine line identifier information from a DSL circuit without using conventional loop current and ring voltages.